The paper deals with the calculation of polycrystalline material effective diffusion coefficients. The polycrystalline material has been simulated by two-phase composite consisting of matrix and spheroidal inhomogeneities. The Mori – Tanaka scheme was used to account interactions between inhomogeneities. The proposed simulation took into account the effect of segregation as well. The paper put forward two models to describe the polycrystalline material. The former considered grains to be inhomogeneities, and grain boundaries to be a material matrix. The latter, in contrast, did the grain boundaries to be inhomogeneities, and the grains to be a material matrix. The simulation results were compared with experimental data. The importance of taking into account the segregation parameter when calculating effective diffusion coefficients of polycrystalline material was shown.